1. Technical Field
This invention relates generally to pistons for internal combustion engines, and more particularly to pistons having an oil cooling gallery.
2. Related Art
Piston constructions having two substantially closed oil cooling galleries are known. These pistons have an annular, radially outer gallery and an open central gallery formed between upper and lower crown portions. The outer and central galleries can be isolated from one another or in fluid communication with one another via oil passages. In addition, it is known to provide pin lubrication passages extending from one or both of the galleries to a wrist pin. The lubrication passages can extend into a wrist pin bore of a pin boss and/or between laterally spaced pin bosses. The outer gallery is particularly effective in cooling a ring belt region of the piston, while the central gallery is particularly effective in cooling a central crown region formed in part by a combustion bowl wall, which is exposed to hot combustion gasses.
Aside from the combustion bowl being exposed to extreme heat, it is also exposed to extreme combustion forces. Accordingly, the combustion bowl wall needs to withstand the extreme combustion forces. With the central cavity being open beneath the combustion bowl wall, there is an unsupported central region of the combustion bowl wall directly above the central gallery. As such, the central region attains its structural support from a radially outer annular wall formed between the outer and central galleries. Accordingly, both the central region of the combustion bowl and the annular wall must be constructed having a suitable thickness and configuration to withstand the combustion forces generated in use.